Acoustic conductance resistance meter is based on the principle of sound equivalent volume design principle, by the acoustic stimulator, acoustic conductance bridge and air pump three major components. The resistance encountered when the sound waves propagate in the medium is called acoustic impedance, and the sound energy transmitted by the medium is called acoustic conductance. When the sound intensity is constant, the greater the impedance of the medium, the smaller the conductance, the two are inverse relationship. The acoustic conductivity of the medium depends on its friction (resistance), mass (inertia) and strength (elasticity). The mass in the middle ear is determined by the weight of the tympanic membrane and the auditory bone and is relatively constant; the stiffness is mainly generated by the pressure of the tympanic membrane, ligaments, middle ear muscle tension and middle ear air, and is easily influenced by various factors and is highly variable. The acoustic conductance test can evaluate the function of the middle ear sound transmission system, inner ear, auditory nerve and brainstem auditory pathway, and can also detect the function of the eustachian tube, which is one of the commonly used objective clinical hearing examination methods. (1) Static acoustic conduction: The difference between the equivalent volume of the tympanic membrane in normal state and when positive or negative pressure is applied to the tympanic chamber, that is, the acoustic conduction value, represents the activity of the middle ear sound transmission system, but should be combined with the stapedius muscle acoustic reflex and pure tone audiometry for comprehensive analysis. (2) Tympanic chamber conductance map: The dynamic changes in the sound compliance of the tympanic membrane during the continuous gradual adjustment of the air pressure in the external ear canal from +200 to -200 mmH2O are recorded, and the result is the tympanic chamber conductance map, also known as the sound compliance map or tympanic chamber function curve. Type A is a normal curve; Type As is seen in otosclerosis, fixation of the auditory bone or obvious thickening of the tympanic membrane; Type Ad is seen in interruption of the auditory chain, atrophy of the tympanic membrane, healing perforation and abnormal opening of the eustachian tube; Type B is mostly seen in fluid accumulation in the tympanic chamber and obvious adhesions in the middle ear; Type C indicates eustachian tube dysfunction and negative pressure in the tympanic chamber. 2. Stapedius muscle reflex When the human ear is stimulated by a certain intensity of acoustic stimulation, it can cause a reflex contraction of the stapedius muscle, including two pathways of ipsilateral and contralateral acoustic reflex. The normal sound intensity (i.e., acoustic emission threshold) for inducing the stapedius muscle reflex is 70-100 dB (SL), and the left and right ears can induce the ipsilateral and contralateral acoustic reflexes, respectively. Its clinical significance includes: estimation of hearing sensitivity, identification of the nature of deafness, determination of loudness reverberation and pathological adaptation, identification of non-organic deafness, diagnostic reference for determining the site of deafness lesion, localization and diagnosis of peripheral facial palsy, auxiliary diagnosis of myasthenia gravis and assessment of therapeutic efficacy, etc.